Fluorescent lighting fixtures are well-known, and offer several advantages over other types of lighting fixtures such as incandescent lighting fixtures. Fluorescent lamps are more efficient, have a longer life, and run much cooler than incandescent lamps. These advantages make fluorescent lamps very attractive in many situations, particularly where it is desired to save energy without sacrificing light output.
The fluorescent lamp is a low-pressure gas discharge source in which light is produced predominantly by fluorescent powders activated by ultraviolet energy generated by a mercury arc. The lamp contains mercury vapor at low pressure with a small amount of inert gas for starting. The inner walls of the lamp are coated with fluorescent powders commonly called phosphors. When the proper voltage is applied to the lamp, an arc is produced by current flowing between the lamp electrodes through the mercury vapor. This discharge generates some visible light, but mostly invisible ultraviolet radiation. The ultraviolet radiation excites the phosphors to emit visible light.
Like most gas discharge lamps, fluorescent lamps must be operated in series with a current limiting device commonly called a ballast. The ballast limits the current to the value for which each lamp is designed, and also provides the required starting and operating lamp voltages. Fluorescent lamp ballasts typically comprise a transformer having a laminated core and coils, and a capacitor closely associated with the transformer to provide power factor correction. In order to protect the transformer and associated capacitor from physical damage, they are usually enclosed in a housing. Wires extend from the housing to enable the ballast to be connected between the power mains and the fluorescent lamp.
In the past, the ballast was mounted closely adjacent the lamp. In may cases, where there is adequate room (such as for overhead lighting fixtures in buildings) this is not a problem. However, in recent years there has been a surge in the popularity of fluorescent lamps which can be readily substituted for incandescent lamps, such as in table lamps, wall-mounted fixtures, and the like. In those cases, it is desired that the fluorescent bulb be as small as possible, preferably about the same size as the incandescent bulb it is intended to replace. It is also desirable that the fluorescent lamp be readily substitutable for the incandescent lamp. This has led to the development of fluorescent lamps which include the ballast as part of the lamp assembly. It has also led to a great deal of interest in adapting fixtures for incandescent lamps to fluorescent lamps.
One drawback of this type of fluorescent lamp assembly is that it is not suitable for use in problem environments, such as outdoors or even indoors in locations of high humidity. To enable such lamp assemblies to be used in problem environments, either the lamp must be sealed against the environment or the fixture in which it is used must be so sealed. This would require enormous retooling expense to adapt existing lamp assemblies and existing fixtures to make them suitable for use with fluorescent lamps in problem environments.
The present invention solves this problem by locating the ballast inside a standard electrical box, which enables fluorescent lamps to be readily used in conventional fixtures in problem environments without the need for sealing either the lamp assembly or the fixture in which it is used. This permits standard fluorescent lamps and standard lighting fixtures to be used in problem environments without having to modify the fixture except to provide it with a socket appropriate for the fluorescent lamp. Thus, major retooling expense is avoided, and the resulting fixture retains the appearance of a conventional incandescent lighting fixture.